Gettering system for electron tubes



P. D. PORTA Dec. 5, 1967 GETTERING SYSTEM FOR BLECTRON TUBES Filed Oct. 2l. 1964 i.gd W Y United States Patent O 3,356,436 GETTERING SYSTEM FOR ELECTRON TUBES Paolo Della Porta, Milan, Italy, assignor to S.A.E.S. Getters S.p.A., Milan, Italy, a company of Italy Filed Oct. 21, 1964, Ser. No. 405,508 Claims priority, application Italy, Apr. 11, 1964, 7,935/64, Patent 720,119 6 Claims. (Cl. 31625) The subject matter of the present invention is a gettering system for electron tubes both in the phase of testing and in the successive phase of use of the said tubes. This'system is effected by means of a nonevaporating metal absorber, which in the specification andsubsequent claim-s will be indicated by the name bulk getter, and also by means'of a main absorber, indicated simply as ash getter, which is evaporable and preferably of the barium type.

It is well-known that complex electronic devices such as cathode ray tubes, kinescopes for black and white or color TV, oscilloscope tubes, radar display tubes, etc., require long and complicated control tests after production, to evaluate cathode activity, grid and electron alignment, open welds, screening, and other electrical and mechanical properties. Such testing results in the rejection of from to 20% of the tubes.

The usual production technique for electron tubes is at the present time as follows: after depositing the phosphors, lacquering, aluminizing and/or graphitizing the tube, the gun is welded onto the neck and the tube is ready for the pumping process. It should be noted that the cost of screening the tube, especially in the case of a kinescope for color TV, may be as much as 50% of the total cost of the finished tube. The tube is then -subjected to a normal pum-ping cycle, i.e. it is pumped, degassed, the cathode is processed and the tube sealed oi after which, normally, when the tube has cooled a ash getter contained within the tube itself is evaporated. The function of the flash getter is that of further reducing the gas pressure in the tube after it has been sealed off, and also that of maintaining a low internal pressure for the entire life of the tube. The getter generally used in such .tubes is a barium getter which, when ilashed, deposits on the entire inside surface of the tube, .with the exception of the gun, a thin film `of pure barium. lt is this film that acts as a pump for the tube. The greater the amount of barium deposited andthe greater the area of the film thus formed, the better will be the internal pumping action taking place in the tube.

Such a gettering system, however, presents certain dificulties, as follows: acceptance tests of the tube cannot be performed if the barium film is not present, since in such a case the tube could not be made to work satisfactorily. The consequence of this is that tubes rejected because of defects not imputable to screening, when opened to atmospheric pressure forcorrection of the defects, will present a lm of oxidized and carburized barium.

It is well-known that the recovery of these tubes, without elimination of the previously deposited barium, leads to unsatisfactory results because of the particles detached from the barium film which are present in the tube; for this reason the only recoverable part of the rejected tubes is the glass bulb, and this only after adequate washing and rinsing. The foregoing is naturally also true in the case of phosphor, graphite or aluminum defects. However, for the great majority of tubes (around 90%), rejection is due to poor cathodes, to bad beam alignment and analogous defects; in such cases, if the defect could be located before evaporating the barium flash getter a great advantage would be obtained thus favorably aifecting production costs.

3,356,436 Patented Dec. 5, 1967 A method for overcoming these last-mentioned defects would be that of replacing 4the barium getter with a bulk getter. The latter, however, would not be sufiicient to insure the long life of the tube since at the present time the known types of bulk getter have absorption characteristics that are not comparable with those of large-size barium films of the type nowV commonly in use. Nevertheless, a bulk getter of the known type will in most cases suiiice to maintain the required degree of vacuum for the length of time needed to perform the acceptance test in respect of the previously mentioned various types of electronic devices. To this end, the action of the bulk getter can be encouraged by a particular gaseous ambient which it can produce. In particular, it is well known that the presence of a certain quantity of hydrogen is benecial to the action and life of the cathode. The most recent experience has, moreover, shown that a gaseous ambient of this kind can greatly assist in creating the best conditions for the tube acceptance test. In the present invention, therefore, there is conceived a system as defined heretofore, characterized by the fact that, after adopting a method in itself already known for the production of the vacuum in the tube, the bulk getter and the main evaporable ash getter are activated, separately and successively, more exactly as follows: first the bulk getter is activated and then, after a test of the tube giving positive results, the main flash getter is evaporated.

The bulk getter will be especially advantageous if lpartially saturated with hydrogen which, on activation, is liberated within the electron tube in a controlled and known quantity, in such a way as to produce and maintain the conditions most favorable for the activation of the cathode and for the performance of the test.

The practical utility of a technique of this kind, the main purpose of which is to reduce the costs deriving from defective tubes, depends on the absorption rate of the bulk getter in respect of the residual gases, on the careful dosing of the hydrogen required in the electron tube and on the possibility of obtaining, after a positive test and by means of the main evaporable ash getter, a complementary action such as will produce those ambient conditions most likely to insure the long life of the cathode-conditions that neither of the two getters could produce by itself.

It is quite true that in a previous patent No. 3,195,716,y

there is described the fact that the best cathode ambient conditions are produced by the simultaneous activation of a bulk getter and of an ordinary evaporable flash getter, both contained in an electron tube.

It ought, however, to be stresed that, according to the present invention, when activation of the bulk getter iS effected the main evaporable ash getter should remain in the inactivated state, i.e. should not be evaporated. At this point, if the test of the electron tube proves positive, the main flash getter is evaporated. If, on the other hand, the test proves negative, then, on opening the tube to remedy any defects, there is no need to effect on the said tube any lwashing and rinsing operations which, as already stated, are necessary according to the usual technique; and all the -diiculties arising from the presence of the barium film deposited on the inner walls of the tube will be avoided. In fact, before re-closing the tube it will be sufficient to replace the bulk getter with a new bulk getter that has not yet been activated, after which operation there is effected action similar to that already described.

The bulk getter used according to the present invention preferably includes metals or alloys of the elements Zr, Ti, H, Th, W, Mo, Nb, and especially such elements alloyed with aluminum.

The hydrogen content in the bulk getter is between 5 and 15 cc. torr/mg. of thealloy used in the bulk getter. The main evaporable getter used in the tube can be any one of those commonly used having the essential characteristic of being able to evaporate barium over the largest possible area.

In order to make clear the disposition of the two different getters used in the electron tube to effect the system according to the present invention, referenceof a purely illustrative and now limiting kind-is made to the attached drawing, in which FIGS. 1, 2 and 3 represent three different dispositions of bulk getter mounting. The bulk getter is indicated in the drawing with the numeral 1, with the main evaporable flash getter being indicated with the numeral 2. As may be seen, the bulk getter which in the example illustrated has the form of a tablet, and the main flash getter which according to known techniques is ring-shaped, are mounted in different positions in each of the three figures, but are always so disposed as to bring it about that the plane substantially containing the bulk getter is perpendicular to the plane containing the ring of the main flash getter, so that when one getter is activated by means of a high frequency coil, the eddy currents induced into the other getter will not suffice to activate it.

In conclusion, there is now given a practical example of realization of the system according to the invention. In a 23 cathode ray tube for color TV there is mounted, for example, in one of the ways illustrated in the figures of the attached drawing, a flash getter consisting of a ring with an external diameter of 25 mm. and capable of supplying 100 mg. of evaporated barium, and there is also mounted a bulk getter having a surface area of 50 mm.2 and containing 500 cc. torr of hydrogen. After having prepared the tube, after producing the vacuum, and after sealing off the said tube, the bulk getter only is activated. Despite the fact that the vacuum is only about 1x104t torr, a .good cathode activity was found. Because of the presence of hydrogen in equilibrium with the bulk getter, the vacuum cannot be improved; however, the composition of the gas contained in the tube is of the nature necessary to maintain a good activity of the cathode. In the tests performed, the bulk getter used showed that it was suitable to keep the tube in good working condition for a long period of time. In fact, even ten days after activation of the bulk getter it was noted that the pressure had remained constant, and that the activity of the cathoderwas still good.

At this point, when the tube, on testing, proves to be free from mechanical and electrical defects, the barium getter can be evaporated; the successive tube duration tests will prove satisfactory.

4 What is claimed is: 1. A method for the manufacture of an electron tube whereby deposition of a getter metal film on internal surfaces within the tube is avoided until after the tube has tested satisfactorily, said method comprising in sequence the steps of mounting in said tube a first getter device and a second getter device said first getter device having a heat activatable nonvaporizing gas adsorptive getter material, and said second getter device having a getter metal which is evaporable under the inliuence of heat in a vacuum, sealing the tube, activating the first getter device and testing the tube whereby, if the tube tests satisfactorily, the getter metal in the second getter device is vaporized depositing itself in the form of a gas adsorbtive film on the internal surfaces within the tube.

2. A method as claimed in claim 1 comprising saturating the first getter device with hydrogen to enhance its effectiveness independently of the second getter device.

3. A method as claimed in claim 2 wherein the first getter device includes a component selected from the group consisting of Zr, Ti, Th, W, Mo, Nb, Al and alloys thereof.

4. A method as claimed in claim 2 wherein said first getter device included 5.-15. ce. torr/mg. of hydrogen.

5. A method as claimed in claim 1 comprising mounting the getter devices in respective positions whereat only one getter device at a time can be activated by high-frequency heating.

6. A method for the manufacture of an electron tube whereby deposition of a getter metal film on internal surfaces Within the tube is avoided until after the tube has tested satisfactorily, said method comprising in sequence the steps of mounting in said tube a first getter device and a second getter device said first getter device having a heat activatable nonvaporizing gas adsorptive getter material, and said second getter device having a getter metal which is evaporable under the influence of heat in a vacuum, sealing the tube, activating the first getter device and testing the tube whereby, if the tube tests unsatisfactorily the tube is opened to the atmosphere, repaired, sealed, tested, and if the tube then tests satisfactorily the getter metal in the second getter device is then vaporized.

References Cited UNITED STATES PATENTS 1,752,747 4/ 1930 Lederer 316-25 X 1,883,174 10/1932 Von Wedel 316-25 X BICI-IARD EANES, IR., Primary Examiner.l 

1. A METHOD FOR THE MANUFACTURE OF AN ELECTRON TUBE WHEREBY DEPOSITION OF A GETTER METAL FILM ON INTERNAL SURFACES WITHIN THE TUBE IS AVOIDED UNTIL AFTER THE TUBE HAS TESTED SATISFACTORILY, SAID METHOD COMPRISING IN SEQUENCE THE STEPS OF MOUNTING IN SAID TUBE A FIRST GETTER DEVICE AND A SECOND GETTER DEVICE SAID FIRST GETTER DEVICE HAVING A HEAT ACTIVATABLE NONVAPORIZING GAS ADSORPTIVE GETTER MATERIAL, AND SAID SECOND GETTER DEVICE HAVING A GETTER METAL WHICH IS EVAPORABLE UNDER THE INFLUENCE OF HEAT IN A VACUUM SEALING THE TUB, ACTIVATING THE FIRST GETTER DEVICE AND TESTING THE TUBE WHEREBY, IF THE TUBE TEST SATISFACTORILY, THE GETTER METAL IN THE SECOND GETTER DEVICE IS VAPORIZED DEPOSITING ITSELF IN THE FORM OF A GAS ADSORBTIVE FILM ON THE INTERNAL SURFACES WITHIN THE TUBE. 